This invention relates to a process of producing shaped bodies from mixed dusts, which contain substantially iron oxide and are dry or moist or become available in the form of mud and at least one of which has or assumes thixotropic properties.
When gases are purified in industrial plants, the separated substances become available as dry dust or mud or filter cake, in dependence on the purifying method which is used. These waste materials may vary greatly in physical properties even though they often have identical constituents, which may well be utilized further.
A typical example is the solids which are separated in the purification of gases in blast furnace and steel-making plants in the iron and steel industries. These solids contain iron, zinc, and lead and may become available as dry dust or as mud.
When these materials are to be processed further for a recovery of their metal content by a thermal treatment, it is necessary in most cases to shape the materials into bodies, e.g., by pelletizing, sintering or briquetting. Besides, it is desirable to jointly process those materials which become available in different plants and contain the same useful components. For this purpose, these materials must be mixed with each other before they are shaped into bodies because a starting material of uniform composition is desired for the further processing.
The mixing operation will not involve serious problems if the components in question are available in a dry state or in the form of mud. In the latter case, they may be jointly filtered to produce a homogeneous mixture. In some cases it may be suitable to filter both materials separately and then to feed them at metered rates to the subsequent process steps. This practice will be desirable if the individual components vary in rate and properties.
In most cases, however, it is desired to mix dusts and muds and the material discharged from filter presses and drums. The previous practice has been to dry the materials, to comminute the dry materials, and to homogenize the comminuted materials.
The mixing of moist dusts with each other and the mixing of dry and moist dusts and of muds sometimes involves considerable difficulties, particularly if one of the dusts tends to be thixotropic. The conventional mixing units, such as edge runner mixers, screw mixers, double shaft mixers, etc. are not satisfactory in such cases. The mixture has a pulplike, slimy consistency and further processing thereof is virtually impossible. The drying of such mixtures and of non-thixotropic dusts often results in a lumpy material, which must be subsequently ground and then be remoistened before or during the shaping step. This procedure is very complicated and uneconomical.